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gpg: More carefully encode a packet's length.

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* g10/build-packet.c (write_header2): Make sure the length bits are
cleared.  Fail if HDRLEN is set and the specified length can't be
encoded in the available space.

--
Signed-off-by: Neal H. Walfield <neal@g10code.com>
This commit is contained in:
Neal H. Walfield 2016-02-25 21:20:32 +01:00
parent 105a5629c7
commit 960f5e26f2
1 changed files with 8 additions and 1 deletions
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9
g10/build-packet.c
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@ -1450,6 +1450,10 @@ write_header2( IOBUF out, int ctb, u32 len, int hdrlen )
/* An old format packet. Refer to RFC 4880, Section 4.2.1 to /* An old format packet. Refer to RFC 4880, Section 4.2.1 to
understand how lengths are encoded in this case. */ understand how lengths are encoded in this case. */
/* The length encoding is stored in the two least significant bits.
Make sure they are cleared. */
log_assert ((ctb & 3) == 0);
log_assert (hdrlen == 0 || hdrlen == 2 || hdrlen == 3 || hdrlen == 5); log_assert (hdrlen == 0 || hdrlen == 2 || hdrlen == 3 || hdrlen == 5);
if (hdrlen) if (hdrlen)
@ -1462,10 +1466,13 @@ write_header2( IOBUF out, int ctb, u32 len, int hdrlen )
/* 01 => 2 byte length. If len < 256, this is not the most /* 01 => 2 byte length. If len < 256, this is not the most
compact encoding, but it is a correct encoding. */ compact encoding, but it is a correct encoding. */
ctb |= 1; ctb |= 1;
else else if (hdrlen == 5)
/* 10 => 4 byte length. If len < 65536, this is not the most /* 10 => 4 byte length. If len < 65536, this is not the most
compact encoding, but it is a correct encoding. */ compact encoding, but it is a correct encoding. */
ctb |= 2; ctb |= 2;
else
log_bug ("Can't encode length=%d in a %d byte header!\n",
len, hdrlen);
} }
else else
{ {